ATWS Characteristics of Super LWR with/without Alternative Action

Anticipated-transient-without-scram (ATWS) of the supercritical-pressure light water cooled thermal reactor with downward-flow water rods (Super LWR) is analyzed to clarify its safety characteristics. At loss-of-flow, heat-up of the fuel cladding is mitigated by the water rods removing heat from the fuel channels by heat conduction and supplying their coolant inventory to the fuel channels by volume expansion. The average coolant density is not sensitive to the pressure due to the small density difference between “steam” and “water” at supercritical-pressure. Closure of the coolant outlet of the once-through system causes flow stagnation that suppresses an increase in the coolant density due to an increase in the temperature. Therefore, the increase in power is small for pressurization events. The coolant density and Doppler feedbacks provide good self-controllability of the power against loss-of-flow and reactivity insertion. An alternative action is not needed either to satisfy the safety criteria or to achieve a high-temperature stable condition for all ATWS events. Initiating the automatic depressurization system is a good alternative action that induces a strong core coolant flow and inserts a negative reactivity. It provides an additional safety margin for the ATWS events. Even the high core power rating of the Super LWR has excellent ATWS characteristics, providing a key reactor design advantage.

[1]  Yoshiaki Oka,et al.  Improved core design of the high temperature supercritical-pressure light water reactor , 2004 .

[2]  Yoshiaki Oka,et al.  Refinement of Transient Criteria and Safety Analysis for a High-Temperature Reactor Cooled by Supercritical Water , 2001 .

[3]  S. Koshizuka,et al.  Numerical analysis of deterioration phenomena in heat transfer to supercritical water , 1995 .

[4]  Allan F. Henry,et al.  Nuclear Reactor Analysis , 1977, IEEE Transactions on Nuclear Science.

[5]  Yoshiaki Oka,et al.  Three-dimensional Core Design of High Temperature Supercritical-Pressure Light Water Reactor with Neutronic and Thermal-Hydraulic Coupling , 2005 .

[6]  Yoshiaki Oka,et al.  Principle of rationalizing the criteria for abnormal transients of the Super LWR with fuel rod analyses , 2006 .

[7]  D. Spalding,et al.  A calculation procedure for heat, mass and momentum transfer in three-dimensional parabolic flows , 1972 .

[8]  Y. Oka,et al.  Fuel and Core Design of Super Light Water Reactor with Low Leakage Fuel Loading Pattern , 2006 .

[9]  S. Koshizuka,et al.  Flow-Induced Accident and Transient Analyses of a Direct-Cycle, Light-Water-Cooled, Fast Breeder Reactor Operating at Supercritical Pressure , 1996 .

[10]  T. Fujii,et al.  Forced convective heat transfer to supercritical water flowing in tubes , 1972 .

[11]  S. Koshizuka,et al.  Fuel Design of High Temperature Reactors Cooled and Moderated by Supercritical Light Water , 2003 .

[12]  Shigeaki Nakagawa,et al.  Safety demonstration tests using high temperature engineering test reactor , 2004 .

[13]  Yue Fen Shen,et al.  An investigation of crossflow mixing effect caused by grid spacer with mixing blades in a rod bundle , 1991 .

[14]  S. Koshizuka,et al.  Control of a High Temperature Supercritical Pressure Light Water Cooled and Moderated Reactor with Water Rods , 2003 .

[15]  Yoshiaki Oka,et al.  LOCA Analysis of Super LWR , 2006 .

[16]  Yoshiaki Oka,et al.  Safety of Super LWR, (I) Safety System Design , 2005 .

[17]  Warren M. Rohsenow,et al.  Film boiling on the inside of vertical tubes with upward flow of the fluid at low qualities , 1963 .